The chemical element technetium has the atomic number 43 and the letter Tc as its symbol. It is the lightest element with radioactive isotopes. Technetium is produced as a synthetic element only when needed. The most common sources of naturally occurring technetium are uranium and thorium ores, which produce it spontaneously by fission, or molybdenum ores, which produce it by neutron capture. Located between the elements rhenium and manganese in group 7 of the periodic table, the chemical properties of this crystalline, silvery-gray transition metal are midway between those of the two nearby elements. 99Tc is the most common isotope, naturally occurring only in trace amounts.
Nuclear medicine uses technetium-99m, a short half-life nuclear isomer that emits gamma rays, for a number of procedures, including the diagnosis of bone cancer. The ground state of technetium-99 is used as a source of beta particles that do not emit gamma rays. Commercially produced long-lived technetium isotopes are obtained from nuclear fuel rods and are byproducts of the fission of uranium-235 in nuclear reactors. The discovery of technetium in red giants in 1952 contributed to the demonstration that stars can create heavier elements because even the technetium isotope with the longest half-life (4,21 million years) is relatively short.
Technetium History
Early versions of the periodic table proposed by Dmitri Mendeleev, from the 1860s to 1871, had a gap between molybdenum (element 42) and ruthenium (element 44). Mendeleev predicted in 1871 that this missing element would fill the space below manganese and would have a similar chemical structure. Because the predicted element was one position lower than the known element manganese, Mendeleev gave it the intermediate name "ekamanganese" (from the Sanskrit word "eka" meaning "one").
Before and after the publication of the periodic table, many early scientists were eager to be the first to find and describe the missing element. Based on the layout of the table, it should be easier to find than other undiscovered elements.
Elements 75 and 43 were discovered in 1925 by German chemists Walter Noddack, Otto Berg, and Ida Tacke. Element 43 was named Masurium in honor of Masuria in East Prussia, which was Walter Noddack's ancestral hometown and is now part of Poland.
The name caused great hostility in the scientific community, as the German army defeated the Russian army in the Masuria region during the First World War. As the Noddacks continued to hold academic posts while the Nazis were in power, suspicion and hostility to claims to discover element 43 continued. The team used a beam of electrons to detonate the columbine, and by analyzing the X-ray emission spectrograms, they were able to determine that element 43 was present. In 1913, Henry Moseley developed a formula relating the atomic number to the wavelength of the X-rays produced. The team claimed to have discovered a weak X-ray signal at a wavelength associated with element 43.
Later experimenters were unable to confirm this discovery, so it was considered false. Nevertheless, element 1933 was referred to as masurium in a series of articles on the discovery of the elements published in 43.
However, Paul Kuroda's research on the amount of technetium that can be found in the ores they studied - an amount of 3 × 10−11 μg/kg of ore would not have passed and thus could not be detected by the Noddacks' methods - refuting some more recent attempts to justify the Noddacks' claims.
Carlo Perrier and Emilio Segrè conducted an experiment at the University of Palermo in Sicily in 1937 that proved the existence of element 43.
During his trip to the United States in mid-1936, Segrè visited Columbia University in New York and the Lawrence Berkeley National Laboratory in California. He persuaded Ernest Lawrence, the creator of the cyclotron, to allow the device to return some of its radioactive remains. A piece of molybdenum foil from the cyclotron's deflector was mailed to him by Lawrence.
Segrè enlisted the help of his colleague Perrier to show, through comparative chemistry, that the activity of molybdenum was indeed due to an element with atomic number 43. In 1937 they succeeded in separating technetium-95m and technetium-97.
University of Palermo officials asked them to name their discovery "panormium" in honor of the city's Latin name, Panormus. Since element 43 was the first element created artificially, it was given the name "artificial" in 1947, derived from the Greek word for v. Segrè visited Berkeley once again and ran into Glenn T. Seaborg. They identified Technetium-99m, a metastable isotope that is currently used in about ten million medical diagnostic procedures per year.
Technetium's spectral signature was discovered in 1952 by Californian astronomer Paul W. Merrill in light from S-type red giants.
Although the stars were about to die, the short-lived element was abundant; This showed that the element was created through nuclear processes inside the stars.
These data supported the idea that nuclear synthesis of stars produces heavier elements. Such observations have recently provided evidence that elements form through neutron capture in the s-process.
Since then, numerous efforts have been made to find natural sources of technetium in terrestrial minerals.
Technetium-238, which occurs as the spontaneous fission byproduct of uranium-99, was isolated and identified in 1962 at extremely small levels (about 0,2 ng/kg) in pitchblende in the Belgian Congo. There is evidence that substantial quantities of technetium-99 are produced in the Oklo natural nuclear fission reactor and subsequently converted to ruthenium-99.
Physical Properties
Technetium is a radioactive metal that resembles platinum in appearance and typically occurs as a gray powder. The crystal structure of the nanodisperse pure metal is cubic, while the crystal structure of the bulk pure metal is hexagonal closely packed. The Tc-99-NMR spectrum of hexagonal stack technetium is divided into 9 satellites, while that of nanodisperse technetium is not. Distinctive emission lines of atomic technetium are found at wavelengths 363.3 nm, 403.1 nm, 426.2 nm, 429.7 nm, and 485.3 nm.
Since magnetic dipoles in metal form are only weakly paramagnetic, they align with external magnetic fields, but adopt random orientations when the field recedes. Pure, metallic, single-crystal technetium transforms into a type-II superconductor at temperatures less than 7,46 K. Technetium has the highest depth of magnetic penetration of any element except niobium below this temperature.
Source: Wikipedia
Günceleme: 08/05/2023 13:11